Rotating double acting chuck cylinder for machine tools

ABSTRACT

A CHUCK ACTUATING DEVICE HAVING A BODY WITH A CYLINDRICAL CAVITY AND A DOUBLE ACTING PISTON IN THE CAVITY. A MAIN COMPRESSED AIR PASSAGE SUPPLIES AIR TO THE BODY THROUGH A ROTARY FLUID CONNECTOR AND A FOUR-WAY VALVE IN THE BODY CONTROLS THE SUPPLY OF COMPRESSED AIR TO THE OPPOSITE SIDES OF THE PISTONS. THE VALVE IS SHIFTABLE BY FLUID PRESSURE SUPPLIED THERETO VIA CONTROL PASSAGES ALSO EXTENDING INTO THE BODY THROUGH SAID ROTARY FLUID CONNECTOR. A RESILIENT SEALING RING CHECK VALVE IS INTERPOSED IN THE MAIN AIR PASSAGE UPSTREAM OF SAID FOUR-WAY VALVE

Nov. 16, 1971 G. HECKMANN 3,620,128

Filed Oct. 8, 1969 United States Patent O 3,620,128 ROTATING DOUBLEACTING CHUCK CYLINDER FOR MACHINE TOOLS Gnter Heckmann, Sprockhovel,Germany, assigner to Paul Forkardt Kommanditgesellschaft, Dusseldorf,

Germany Filed Oct. 8, 1969, Ser. No. 864,589 Int. Cl. F1511 1 1 08,13/042 U.S. Cl. 91-446 12 Claims ABSTRACT OF THE DISCLOSURE A chuckactuating device having a body with a cylindrical cavity and a doubleacting piston in the cavity. A main compressed air passage supplies airto the body through a rotary fluid connector and a four-way valve in thebody controls the supply of compressed air to the opposite sides of thepistons. The valve is shiftable by lluid pressure supplied thereto viacontrol passages also extending into the body through said rotary fluidconnector. A resilient sealing ring check valve is interposed in themain air passage upstream of said four-way valve.

This invention relates to a rotary, compressed-airactuated double-actingchuck cylinder for machine tools, and more specifically to a chuckcylinder of this type which has a four-way valve for reversing thedirection of movement of the chuck piston, and with safety means forpreventing a drop in pressure in the cylinder when the supply ofcompressed air is interrupted.

Rotary chuck cylinders for compressed air actuation have a pin rotatingtherewith, on which is mounted a stationary transfer housing for theconnection of the pressure lines. The four-way valve for the reversal isgenerally arranged separately from the cylinder and is connected throughtwo lines with the transfer housing.

If the air pressure fails and no special precautions are provided, thepressure in the cylinder would drop, and would do so instantaneouslywhen a break occurs in the line. If the piston of the cylinder serves toactuate a chuck, a drop in pressure may lead to the release of aworkpiece which would be spun oif during rotation.

It is known to prevent the escape of compressed air from the chuckcylinder by check valves, which close on cessation of the pressuresupply. Obviously it makes no sense to arrange such check valves in thestationary feeding line to or in the transfer housing, since then alsothe transfer from this housing to the rotary pin of the cylinder wouldbe located in that part of the system which is to be blocked by thecheck valve. This transfer is however not always wholly huid-tight andthe leak may in the course of time become greater due to wear withoutcausing difficulties during normal operation. However, on the cessationof the compressed air supply the air would in these circumstances escapeat a more or less fast rate, and a shut-off would hardly help. It is forthis reason that, it is customary to provide a check valve for eachcylinder chamber directly on or in the cylinder or in the rotary pin. Inorder to make sure, when it is desired to release all pressure from thecylinder, that the compressed air can properly escape from saidcylinder, it is necessary that the associated check valve be held openas long as necessary. To this end, in the heretofore known designs, eachcheck valve is controlled by one auxiliary piston, or both check valvesare controlled by an auxiliary piston common thereto. The auxiliarypiston or pistons are for this purpose actuated by the actuatingpressure for the respective other cylinder chamber.

These known arrangements of rotary chuck cylinders with two controlledcheck valves have proved satisfactory rice insofar as even after manyyears of operation, in the case of the cessation of the compressed airsupply in general even after many hours, a suitable operational pressureprevailed in the cylinder.

Rotary chuck cylinders with two check valves controlled by the actuationpressure have, however, two disadvantages, which under certaincircumstances represent considerable drawbacks.

When a drop occurs in the air pressure or the air pressure failscompletely, not only the cylinder chamber which is under pressure butalso the cylinder chamber which is not under pressure will be off. Whenthe two cylinder chambers, for example, through a damaged piston seal,communicate with each other, the pressure between the two pistonchambers may equalize. Such a pressure `equalization reduces thepressure difference generating the chucking force, so that the pistonscan no longer exert a force while this cannot be observed from theoutside. Under these circumstances, depending on the design of the chuckand the work situation, the workpiece may easily be pulled out or spunout, which by means of the check valve should have been specificallyprevented.

In normal operation slight damage to the piston seal will not be harmfulsince a constant connection with the pressure air network exists. Onlyunder the above described circumstances does it become particularlydisadvantageous-however mostly by an accident which was to be avoided.

A further disadvantage of the heretofore known rotary chuck cylinderswith two controlled check valves consists in the too small displacementspeed of the chuck piston on reversal. This results from the fact, thatduring the movement of the piston in the cylinder-mostly only a smallexternal resistance is to be overcome-the pressure difference betweenthe two cylinder chambers is generally very small because the long andnarrow lines throttle the inwardly and outwardly flowing air and becausein view of the control by the auxiliary piston, of the check valve whichcontrol depends on the pressure difference, said check valve is onlyopened slightly. This again means an additional throttling and reductionof the pressure difference. As a result, in particular when working atlow pressure, an important amount of time is lost.

It is, therefore, an objet of the invention to provide a rotarydouble-acting pressure air-actuated chuck cylinder for machine tools ofthe hereinbefore described kind, which will afford an increased securityagainst loss of chuck force during the loss of compressed air and inview of an increased speed of movement of the chuck piston during thereversal will permit a faster and thereby more economical manner ofworking.

These and other objects and advantages of the invention will appear moreclearly from the following specification in connection with theaccompanying drawings in which:

FIG. l is a longitudinal section through an embodiment of a chuckcylinder according to the invention.

FIG. 2 is a longitudinal section through a modified check valve for usein connection with the present invention.

According to the present invention there is provided a rotarydouble-acting chuck cylinder for a machine tool with a four-way valvefor reversing the direction of movement of the chuck piston, which ischaracterized in that the four-way valve is arranged in the rotary partof the chuck cylinder between a single check valve and the cylinderchambers, while the path of the four-way valve for exhausting thecompressed air from the cylinder chambers leads directly on the cylinderhousing into the atmosphere.

The design according to the invention furthermore brings about that thecylinder chamber which is not under pressure, will in case of failure ofcompressed air remain connected with the ambient air, so that even onthe occurrence of an undesired connection between the two cylinderchambers, for example, due to a damaged seal, no pressure equalizationbetween the two cylinder chambers can occur. While in this instance, thepressure in the cylinder chamber in which the chuck force is generated,may drop slowly, it does not build up simultaneously in the otherchamber an increasing pressure, so that the pressure difference givingrise to the chuck force decreases only slightly.

Since the check valve in this arrangement is passed through by fluidonly in one direction there is no need for it to be controlled. Theconnections between the fourway valve and the cylinder chambers areshort and during the reversing operation increased speed of the chuckpiston, also immediately after the start of the reversing operation andalso at low operating pressure.

In view of the arragnement ofi the four-way valve directly ahead of thecylinder chambers, in accordance with the invention, the outlet of thefour-way valve can directly be connected by the shortest path to theOutside air. Consequently a trouble causing throttling of the outwardlyflowing air cannot occur through passages of long bores and ducts.

According to a further feature of the invention the four-way valve isreversed by a pressure medium, which is controlled by a valve outsidethe cylinder housing and is conveyed through special control ducts intothe rotating part through the stationary pressure medium transferhousing.

The four-way valve is according to a further feature of the inventiondesigned as a control slide or valve spool having a sliding direction atright angles to the axis of rotation. This control slide may form a atslide, which lies against a plane slide face under pressure and isdisplaceable between its end positions by a double-acting controlpiston.

According to a further feature of the invention both end positions ofthe control slide and of the control piston are symmetrical to the axisof rotation, and the common center of gravity of both parts passes ateach adjustment position through the axis of rotation.

According to the invention it is further proposed, to provide a certainamount of play or lost motion between the control pistons and thecontrol slide for the four-way valve, so that the control piston at eachreversing action will have a lead and will be able to free or knockloose the control slide, if the latter should stick after long nonuse.In this way, at the same time the distance of its center of gravity fromthe axis of rotation will be increased.

According to the invention it is furthermore proposed as pressure mediumfor the movement of the control piston to employ a fluid which willsimultaneously serve for lubricating the pin journalled in the pressuremedium transfer housing.

With regard to the construction of the embodiment of the check valve, itis proposed in accordance with the invention to form the check valve byan elastic ring which is so arragned that it flexes elastically underthe influence of the inflowing compressed air, but springs back orreturns to its original shape and position, when the flow ceases, and ispressed by the pressure prevailing in the space therebehind against asealing surface.

The check valve may be made integral or of one piece with the pin, whichby means of a ange is secured to the intermediate housing containing thefour-Way Valve and contains a central supply or feed bore. Such anembodiment employs an O-ring, which is coaxial with the axis of rotationand is located in a groove having a wedgeshaped cross section. Thebottom of said groove is through at least one radial bore incommunication with the central supply bore in the pin of the cylinderhousing. Another embodiment of the check valve may be in the form of agrooved ring the open side of which faces away from the in-flowdirection so that its elastic lip offers a resistance only to the returnow of the air but elastically flexes under the influence of the inowingair.

The advantages of the double-acting chuck cylinder according to theinvention are as follows:

Increased safety in case of network failure or line break, since notonly is the compressed air prevented from escaping from the respectivecylinder chamber under pressure, but also a substantially reducedpressure equalization between the two cylinder chambers will beprevented. The movement of the chuck piston is not slowed down becauseof long ducts or lines and additional throttling areas in the path ofthe exhaust air. For the reversal operations only small quantities of apressure medium are necessary so that for this purpose thin pipes andsmall control valves will sufce. For the reversing operations, oil maybe employed, which serves at the same time for lubricating the runningand sealing surfaces of the pressure medium transfer housing. Whilst thecylinder rotates, accidental or undesired adjustments or displacementsof the control slide are not possible. Finally only one check valve isrequired that does not have to be controlled and, therefore, can bedesigned extremely simple and safe in operation.

For this purpose, it is proposed in accordance with the invention thatthe check valve be made in one piece with the pin, which by means of aflange is secured to an intermediate housing containing the four-wayvalve. Simultaneously, the slide face may be formed on an insert securedwithin the cylinder housing which insert contains the connecting andtransfer passages for the supply and exhaust of compressed air.

Referring now to the drawings in detail, the chuck cylinder, which issecured to the spindle (not illustrated) of a machine tool comprises acylinder housing 1, which is closed by a cover 2, and has a chuck piston3 slidable therein. The chuck piston 3 is provided with a piston rod 3awhich transmits the movements and the force of the chuck piston 3through the spindle to that part of the machine tool which is to beactuated, for example, the chuck jaws.

The movement of the chuck piston 3 is effected by compressed air, whichis introduced into one of two cylinder chambers 4a and 4b. The supply ofcompressed air to the rotary cylinder housing 1 is effected through apressure-medium transfer housing 7, which is supported on a pin 6 of thecylinder housing 1 and which delivers the compressed air suppliedthrough a connection 8, into a central bore 11 in the pin 6. For thispurpose, the stationary pressure medium delivery housing 7 is providedwith an annular groove 7c, into which opens the connection 8 and whichthrough a bore, remains in continuous communication with the centralbore 11.

The pin 6 carries a ange 6a by which it is secured to an intermediatehousing 5, which in its turn is disposed on the outer end of thecylinder housing 1. A four-way valve 13 is arranged in this intermediatehousing 5 and comprises a control slide 13a and a control piston 13e.The piston 13C is arranged in a through bore in the intermediate housing5, which bore is closed at its ends by means of closure members 5a. Thecontrol slide 13a is biassed by a spring 13b against a slide surface 14din which the passages of the four-way valve 13 are disposed. Theconnection between the control slide 13a and the control piston 13e` isnot positive, since the pin of the control slide 13a has a smallerdiameter than the pinreceiving bore in the control piston 13e. This isclearly apparent from the longitudinal section of FIG. l. In view ofthis arrangement, the control piston 13C will prior to each adjustmenttravel over a short idle or dead path, as a result of which the controlpiston 13e will be able to knock loose or free the control slide 13a, ifthe latter should have become stuck after a long period of nonuse.

In the illustrated embodiment, the slide face 14d is formed on an insert14, which is with a flange 14C inserted into the cylinder housing 1 andwhich in addition to the communication passage 14b to the rear face ofthe cylinder chamber 4b additionally has a transfer passage 14a to thefront cylinder chamber 4a. Since the transfer passage 14a leads into acentral chamber 3c of the piston rod 3a, the piston rod 3a has aradially extending transfer bore 3b which leads to the front cylinderchamber 4a. That passage of the four-way valve 14 which serves forexhausting compressed air from the cylinder chambers 4a and 4b, leads inthe illustrated embodiment to an exhaust bore 14e in the cylinderhousing 1 which bore 14e communicates with the atmosphere.

A check valve 12 is arranged in the central bore 11 for the compressedair which bore 11 leads to the fourway valve 13. This check valve 12comprises in the embodiment illustrated in FIG. 1, an elastic O-ring12a, which lies in a groove 12b concentric with the axis of rotationX-X, said groove 12b being wedge-shaped in cross-section. The base ofthis groove 12b communicates through a plurality of radial bores 11cwith the central bore 11 as is illustrated in the drawing. As soon asthe pressure in the annular space outside the O-ring 12a exceeds thepressure in the central bore 11, the O-ring 12a is pressed into thewedge-shaped groove 12b, so that it will prevent back-flow of thecompressed air in the central bore 11.

In the second embodiment of the chuck valve as illustrated in FIG. 2, inplace of the O-ring 12a, a grooved ring 12d is employed the open side ofwhich faces away from the in-flow direction. The elastic lip of thegrooved ring 12d provides resistance only to the return ow of the air,Whereas it is elastically deformed by the inflowing air.

The movement of the control slide 13a by means of the control piston13e` is effected by the pressure medium, which is supplied to the twoopposing piston faces of the control piston 13c through control passages10a, 10b respectively. These control passages a, 10b lead into the pin 6in the region of the annular grooves 7a, 7b, which are arranged likewisein pressure-medium transfer housing 7 and are in communication with thecontrol passage connections 9a, 9b respectively.

In the forward position of the chuck piston 3 as illustrated in thedrawing, the rear cylinder chamber 4d communicates through the passage14b the four-way valve 13a, the check valve 12 and the central bore 11wi'h the connection 8, so that the chuck piston 3 is held in theillustrated position. By means of the centrifugal force exerted on thecontrol piston 13C and the control slide 13a these two parts of thefour-way valve 13 are held in the illustrated position whilst the chuckcylinder rotates about its axis of rotation X-X.

If through a failure in the compressed air supply or through a rupturein the pressure air passage leading to the connection 8 the pressure inthe central bore drops the check valve 12 would close immediately in asmuch as the O-ring 12a would press into the base of the groove 12b orthe sealing lip of the grooved ring 12d would engage its sealing surfacewhereby the radial bores 12C would be sealed. The cylinder chamber underpressure is thus shut off, and the pressure can drop slowly only as aresult of any leak due to a faulty seal. This would in practice take atleast several hours. The other cylinder chamber remains in communicationwith the atmosphere through the control slide 13a so that the forceacting upon the chuck piston 3 will be maintained. If this chuck piston3 actuates for example a chuck the jaws of which must under nocircumstances be allowed to release the workpiece as long as itsrotates, the fact that the force acting upon piston 3 is maintainedrepresents an active safeguard against accidents.

When the chuck piston 3 is to be reversed from its illustrated positionat the forward end to the rear position, whilst the chuck cylinder isstationary a pressure impulse is exerted through the control passageconnection 9a and the control passage 10a upon the downwardly directedpiston face of the control piston 13C as illustrated in the drawing sothat this piston together with the control slide 13a is displaced beyondthe intermediate position into the opposite end position. In this endposition, the control slide 13a connects the communicating passage 14bwith the outlet bore 14e, whereas the transfer passage 14a is connectedwith the central bore 11. The compressed air provided continuouslythrough the connection 8, through the check valve to the four-way valve,then passes into the transfer passage 14a, the chamber 3c and thetransfer bore 3b in the piston rod 3a of the chuck piston into theforward cylinder chamber 4a. In this way, the chuck piston 3 moves inthe direction of the pin 6 of the chuck cylinder, whilst the compressedair in the rear cylinder chamber 4b is exhausted through thecommunication passage 14b through the exhaust bore 14e into theatmosphere.

Since the four-way valve 13 is located in the rotary part of the chuckcylinder, only one connection 8 is necessary. For reversing the four-wayvalve 13 when the chuck cylinder is stationary, short pressure impulsesare sufficient. If a lubricating fluid is used as pressure medium forreversing the control piston 13a, lubricating fiuid will simultaneouslyserve for lubricating the pin 6 rotating in the fixed pressure-mediumtransfer housing 7. Also, as will be apparent from the drawing, thechuck cylinder is of a particularly simple design, especially withregard to the arrangement of the slide surface 14d on the insert 14, inview of the arrangement of the four-way valve 13 in the intermediatehousing and in view of the simple and yet operationally safeconstruction of the check valve 12.

It is, of course, to be understood thatt he present invention, is, by nomeans, limited to the particular showing in the drawing but alsocomprises any modifications within the scope of the appended claims.

What is claimed is:

1. A device for actuating the chuck of a machine tool and comprising: abody rotatable on an axis and having a cylinder cavity therein, a doubleacting main piston reciprocable in said cavity, a member connected tothe piston to be reciprocated thereby and extending from the body forconnection to a chuck part to be actuated, a spindle fixed to andprojecting from said body on said axis, a sleeve rotatable on saidspindle, a main passage extending through said sleeve and into andaxially along said spindle for supplying compressed air to said mainpiston, a four-way valve in said body interposed between said mainpassage and the opposite sides of said main piston, exhaust passagemeans leading from said fourway valve to the atmosphere, said four-wayvalve being shiftable for selectively connecting a respective side ofsaid main piston to said main passage while connecting the other sidethereof to said exhaust passage means, control means operable forshifting said four-way valve, and means operable for preventing loss ofair pressure to said main piston in the event of interruption of thesupply of compressed air to said main passage, said means for preventingloss of air pressure to said main piston comprising a check valve insaid main passage upstream of said four-way valve, said check valvecomprising a valve seat and cooperating resilient sealing ring mountedon said spindle on said axis and elastically deformable by compressedair flowing in said main passage toward said fourway valve, said spindlenear the end thereof nearest the four-way valve being provided with anannular groove communicating with said main passage at the bottom of thegroove, said resilient sealing ring being mounted in said groove.

2. A device according to claim 1, in which said control means forshifting said four-way valve comprises opposed fluid operable areasconnected to Said valve, and control 7 passages leading through saidsleeve and into and axially along said spindle to said fluid operableareas for supplying fluid thereto.

3. A device according to claim 1, in which said fourway valve comprisesa slide member slidable at right angles to the axis on which said bodyis rotatable.

4. A device according to claim 3,' in which said slide member is flat onat least one side, a valve plate in the body engaging one side of saidmember, passages leading from said valve plate to opposite sides of saidmain piston, a spring urging said slide member toward said plate, and adouble acting control piston operatively connected to said slide plate,the opposite ends of such control piston constituting said opposed uidoperable areas.

5. A device according to claim 4, in which said slide member and controlpiston are symmetrically arranged with respect to said axis and have acommon center of gravity which passes from one side of said axis to theother each time the slide member is shifted.

6. A device according to claim 4, in which the connection between saidslide member and control piston provides for lost motion in thedirection of movement of said slide member.

7. A device according to claim 2, in which the fluid pressure mediumserving for controlling the shifting of said four-way valve is also alubricant.

8. A device according to claim 1, in which the side walls of said groveconverge toward the bottom of the groove and said resilient sealing ringis in the form of an O-ring engaging said side walls of the groove.

9. A device according to claim 1, in which said sealing ring has aresilient lip on one side engaging one wall of said groove and yieldablein response to pressure in the main passage upstream of said groove.

10. A device according to claim 1, in which said exhaust passage meanscomprises a single passage extending from said four-way valve throughsaid body to the atmosphere.

11. A device according to claim 1, in which said groove is formed onsaid spindle at the body end thereof, a housing member mounted on saidbody and containing said four-way valve, and a flange on said spindlemounting the spindle on said housing member.

12. A device according to claim 4, in which said plate is in the form ofan insert mounted in a wall of said body and includes a tubular portionprojecting through said main piston, said passages leading from saidfour-way valve to the opposite sides of said main piston being formed insaid plate and said tubular portion.

References Cited UNITED STATES PATENTS 2,291,147 7/1942 Carlsen 279-42,792,019 5/1957 Lieser 137-625.25 X 2,809,612 10/1957 Highberg 279-4 X3,079,896 3/1963 Johnston 92-106 3,364,823 1/1968 Benjamin et al. 91-4203,369,464 2/1968 Blattry 91-448 X 3,411,415 11/1968 Benjamn et al 91-420MARTIN P. SCHWADRON, Primary Examiner I. C. COHEN, Assistant ExaminerU.S. Cl. X.R. 91-448, 461

